Re- powering my boat

[islander55]

hey there
Ive got a 16.5 larson. It currently has a 1992 yamaha 90hp oil injected outboard on it
Im wanting to put a yamaha 90hp four stroke on but im not sure if that would be to heavy
Heres a picture of how it currently sits as of now with the two stroke on
Also wondering if a 50hp four stroke would be a bit under powerd

 

[scott craven]

I think the 50hp will be a little underpowered.
60-70 hp - 4 stroke will be enough to push your boat.
my 60 Yamaha weighs about 220 lbs
I can get close to 30knots on 16' K&C.

 

[Fishalot]

If your current outboard runs well I wouldn't change it. Those Yamaha 2 strokes are known for being reliable and powerful. It will use more fuel than a 4 stroke but will be more responsive.

 

[Clint r]

http://www.nadaguides.com/Boats

Here's a link to a site that has weight info on outboards.

 

[Damien]

Yip, keep that Yammy.

 

[islander55]

its a gas gozoler though aha

 

[Clint r]

My Yamaha 6hp is a 2 stroke. 100:1 mix and it's nearly smokeless. Use Amsoil mix oil and it might as well be a 4 stroke.

 

[Clint r]

its a gas gozoler though aha

How much gas does it use? My last boat was a 16' k&c and I was running old mercs so not really applicable but I switched out the 85horse for a 115 and actually used less fuel to achieve same speed/distance. Can't remember exact numbers but it was like 8 miles extra(?) per 5 gallons but don't quote me on that. I'll ask the wife later. She might remember exact figures.

 

[islander55]

well if i go full out it will last an hr, and thats doing 35knts not trimmed up

 

[triplenickel]

its a gas gozoler though aha

How much fuel can you buy for the cost of an upgrade? The math on saving money with a new motor usually doesn't work, you'll buy a decades worth of fuel for the upgrade and the upgrade still needs fuel. If you're talking new you could likely buy 7000L of fuel for that price. Just like a car if you want to save money slow down.

 

[fshnfnatic]

Yep,those older 2 smokes burn the fuel.Like Clint r stated you could benefit from going up to a 115 and backing off on the throttle to say 3/4's and you'd find your fuel consumsion go down significantly.I run a 115 on my 16.5 Double Eagle which looks to be
an almost identical hull from the photos I've seen and shouldn't be a problem for you.

 

[islander55]

idk might be getting a suzuki 90hp four stroke for 4500

 

[islander55]

since suzukis are apparently the lightest out board out there so far
ive heard there lighter then etecs to but not sure about that one

 

[triplenickel]

idk might be getting a suzuki 90hp four stroke for 4500

$4500 will buy you 450L of fuel per year for the next ten years. The new one will still need fuel so that gap gets even wider. Just go fishing.

 

[Fishin'Zinn]

When was the last time you did maintenance on it? Plugs, filters, tune up etc. Easy to do yourself if you are a little bit competent with tools. Old pre-mix 2-strokes are almost as simple as a hammer as far as engines go. Those motors will run forever if you take care of them.

I agree with saving money. You're just going to buy a different boat later (everyone does!), I understand those 2-smokes can be loud though too (well, not the new E-tec's). 4 stroke is so quiet.


Anyway, here's my vote... Put one of these 'longtail' setupus on her... I think a big block 454 would get you some good numbers

 

[Gear'n'beer!]

Anyway, here's my vote... Put one of these 'longtail' setupus on her... I think a big block 454 would get you some good numbers


That is fricken awesome!!! I would stick to the little 4 banger diesel though

 

[sly_karma]

How much fuel can you buy for the cost of an upgrade? The math on saving money with a new motor usually doesn't work, you'll buy a decades worth of fuel for the upgrade and the upgrade still needs fuel. If you're talking new you could likely buy 7000L of fuel for that price. Just like a car if you want to save money slow down.

$4500 will buy you 450L of fuel per year for the next ten years. The new one will still need fuel so that gap gets even wider. Just go fishing.

Need I add to these? I bought an old hull/outboard combo for cheap and figured I'd be repowering. But then you look at the numbers and say "wait a sec, I can burn a helluva lot of gas for what it would cost to repower and rig it". Mine is an old premix Johnson 140 and there's no question it burns more gas than an equivalent 4 stroke. But it weighs just a smidge over 300 lb and it can pop the 19.5 hull up on plane in seconds. For about $120 you can add a fuel flow sensor and network it into your GPS to show mpg fuel consumption, an excellent tool for adjusting the trim of the boat and finding the most efficient cruising speed for the conditions. Gas savings meant that small investment paid for itself in the first season.

Now of course any of this has to be considered regarding the condition of your existing engine. Perhaps it's got a cylinder that's getting low on compression, or a leak in tilt/trim hydraulics that'll probably cost some money soon. But if it's basically sound, you could do a lot worse than putting a few bucks into new coils, plugs and plug wires and a good lube and cleanup of the exterior. The commonly used parts are generally cheap and easy to get for the old engines, and they're easy to work on. Take a good look online and find a proper factory shop manual for your exact model and year.

Years ago we ran a 50 hp Merc on a 16.5 Hourston runabout hull and found it underpowered, traded up to a 90 hp. After that it was easy to get on plane and no problem to pull a skier.

 

[Reel Gone]

I personally think a 70 would be a good fit . The OP was just asking about size not to be questioned whether or not he should change it up

 

[islander55]

Got a 90hp suzuki

 

[AlK]

I think a 90 hp 4 stroke might be a little to heavy on that boat especially if you have a kicker and if your fuel tank and battery(s) are in the back. I took a quick look at the spec's for the 90 Yamaha 4 stroke and they weigh around 360 lbs which is only about 60lbs less than my 200 Merc 2 stroke.